Heminger, of course, is referring to worries about the safety of the existing eastern span, part of which collapsed during the 1989 Loma Prieta quake.

State transportation officials say that, as a result of cushion time built into the construction process, they still expect to meet their targeted 2013 date for opening the new eastern span. But at the least, the months of delays caused by questions over the welds are expected to add tens of millions of dollars to the project's price tag.

The welding holdup is reminiscent of the flap four years ago when union whistle-blowers said faulty welds had gone unrepaired inside pilings for the skyway portion of the span. A resulting federal investigation came up empty - but not before it halted bridge work for weeks and cost taxpayers millions.

This time, the welds in question are contained in 900 bridge panels that are being assembled into football field-size deck sections that will stretch across the 1,800-foot-long tower portion. The sections were supposed to have begun arriving from China in October, but now they aren't expected to get here until at least April.

And "that's the best we can do," said Andrew Fremierof the Metropolitan Transportation Commission. "It's more likely this summer."

The panels are being made by the Zhenhua Port Machinery Co. of Shanghai, which is fabricating most of the steel for the $1.4 billion signature tower on behalf of the span's joint-venture builder, American Bridge-Fluor Enterprises. ZPMC, as the company is commonly known, is the same firm that built the mammoth cranes that tower over the Port of Oakland - indeed, it builds 80 percent of the container cranes used around the world.

"This is not a fly-by-night operation, and they couldn't command that kind of market share if they were putting out a shoddy product," Heminger said.

Just to make sure everything was running smoothly, American Bridge put 50 employees on the ground in Shanghai. Caltrans sent another 45 staffers and consulting inspectors to monitor the fabrication process.

Soon after ZPMC started production in late 2007, however, the inspectors hired by Caltrans began finding problems - specifically, an unacceptably large number of welding flaws in the new panels - according to internal agency memos and e-mails turned over to The Chronicle under a Public Records Act request.

In a memo dated March 6, 2008, supervisor Patrick Lowreyof the inspection firm MacTec Engineering and Consulting reported that as many as 65 percent of the more than 30 welded panel sections his office examined - either visually or using ultrasonic testing - failed to meet specifications.

The memos also reveal that the inspectors questioned ZPMC's ability to handle the complex bridge construction job - and that they were frustrated by Caltrans officials' demands that the project proceed despite the allegedly substandard welds.

On March 27, 2008, for example, Lowrey complained to his boss at MacTec, Jim Merrill, that Caltrans had shifted his team's primary inspection role in China "to one of collecting and analyzing data to justify decisions to move the project forward despite not being in compliance."

Lowrey said ZPMC had failed to provide most of the quality control documentation required under its contract with American Bridge and Caltrans, and had failed to produce a single test weld that conformed to the contract specifications.

Four days later, Merrill wrote to Caltrans principal engineer Peter Siegenthalerto complain about the "random weld quality" on more than 100 panels and recommended that the entire production be halted until ZPMC improved its welding process.

Caltrans officials, working with ZPMC and MacTec inspectors, say they eventually worked out a program to tag and repair all the bad welds. But e-mails from inspectors show problems persisted.

On May 23, 2008, MacTec inspector Andy Velascoe-mailed his bosses to say that cracked welds on one deck panel had been replaced, but that the fixes hadn't been tested to make sure they were done right.

On another panel that had been similarly repaired, Velasco wrote, his team did a spot check and found cracks in more than a dozen new welds.

ZPMC officials insisted that the redone welds did not need to be rigorously inspected, Velasco wrote.

Last month, Caltrans dropped MacTec from its three-year, $63 million inspection contract and replaced it with another outfit, Caltrop Corp. Some MacTec officials suspect they were pushed off the job for complaining about the welds, something Caltrans strongly denies.

Caltrans Director Will Kempton said MacTec lost the job when its contract expired, and the state's bridge oversight panel that he serves on recommended putting out the work to competitive bid. Although MacTec was doing a good job, he said, Caltrop came in with a stronger presentation.

Whatever the case, Caltrans says as many as 100 bridge panels are now coming off the ZPMC assembly line each month, and it hopes they'll start arriving in the Bay Area come spring.

After consulting with a structural steel expert from Lehigh University in Pennsylvania, Caltrans officials concluded the decks will be safe, and that the earlier problems were the result of strict weld standards that essentially allowed for no cracks. In other words, a few minor cracks are OK.

"That is the role of the inspectors, to identify issues and problems," Kempton said. "When these issues are raised, we have to deal with them, and that's what we did."

And while "yes, we did modify the acceptance criteria" for the welded bridge sections, Kempton said, "we developed what we think are acceptable standards."

As for how much the delays have added to the bridge's overall price tag? Ultimately, Kempton said, that could depend on just how much time ZPMC can shave off the job by speeding up the remaining fabrication.

"I'm not going to speculate on the costs ... in the paper," Kempton said. "That will be negotiations between the contractor and (us).